Dave,
Agreeing with bobze's post, expanded:
This is the same kind of phenomena that clinicians refer to as "referred pain".
* Let's start with how brain maps for sensory and motor functions are arranged in the brain.
* Sensory and motor maps are topographical, adjacent to each other on the body's surface and generally adjacent to one another in brain maps as well
* These maps change in the brain constantly, are not universal in size, their borders vary from person to person.
* Both sensory and motor maps are part of the cerebral cortex, lying on the brain's surface. See attached thumbnail.
* Brain maps are governed by competition for precious resources, the principle of use it or lose it applies.
* Maps of normal body parts change every few weeks, it is a normal phenomenon.
* A critical concept to grasp for understanding how brain maps (both sensory and motor work). Brain maps are "time based", if you separate signals to neurons in time, you create separate brain maps.
* Maps organize themselves to become topographical and function in a way useful to us.
* Topographical maps emerge in the brain because, nature performs two translations; spatial organization (fingers of the hand for instance) turns into an organized time sequence, which, in turn, turns into a spatial organization (the fingers on the brain map). As proof, a man in France lost both his hands in 1996. He was fMRI scanned as an amputee, showing an abnormal topography in his motor cortex from the loss of his hands. He received a http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1422660/" in 2000, (see attached thumbnail of reattached hands) and fMRI scans were repeated at two, four and six months post operative. The scans revealed his grafted hands came to be recognized and activated normally by the sensory cortex, his motor and sensory maps had reorganized and recreated themselves. Wow.
* Pain is an opinion on an organism's state of health rather than a reflexive response to injury.
* http://en.wikipedia.org/wiki/Ronald_Melzack" wrote the most important article on the history of pain. They contend that the body's pain system is spread throughout the brain and spinal cord, and not a passive recipient of pain, the brain always controls the pain signals we feel. This is know as the "gate control theory of pain", the signals can only travel if the brain gives them 'permission" after being determined they are important enough to be let through.
* Our brain gathers evidence from many resources before triggering pain.
* Neurons in our pain system are plastic, no surprise here, following an injury, the neurons in the pain system fire more easily. Maps can enlarge their receptive field, coming to represent more of the body's surface, increasing pain sensitivity as a result. As these maps change, pain signals in one map can "spill" into adjacent pain maps. As a result we develop what is referred to as: "referred pain", when we are hurt in one body part but feel the pain in another. Sometimes, a single pain single reverberates through the body like a ping pong ball in the brain. The pain persists even after its original stimulus has stopped.
* Here is something to consider in case you need surgery where post operative pain is expected. Post operative phantom pain can be minimized if, nerve blocks or local anesthetics that act on 'peripheral nerves" are applied before general anesthetic is used to put you to sleep. The pain killers administered before surgery appear to prevent plastic change in the brain's pain map that may "lock in" the pain. Amazing.
Rhody...
P.S. All other information from: "The Brain that changes itself" by Norman Doidge.
